Homebrew RF Mixer board for shortwave listening via RTL-SDR.

Did something similar last year but was not successful, the LO and its harmonics trash was all over the spectrum, and had to remove my coax, antenna, and stop all testing later due to construction work at the building. Time to try it again... #SDR #electronics

Not dead yet, still working on the HF Upconverter for shortwave listening. I'll return to retrocomputing and continue working on my Z80 computer again after I managed to get the radio working. #electronics

Found a parasitic oscillation problem at my local oscillator, a lot of RF trash around 70 MHz. #electronics

Mixer v2. Changed random 0603 inductors to 0805 RF inductors with higher Q, hope it can fix the extremely bad loss and unwanted resonance of the filter...

#hamradio #amateurradio

The massive parasitic oscillation and distortion is eliminated, only a little bit of distortion remains, much better now.

#electronics #hamradio #amateurradio

I almost started trying to debug a problem that doesn't exist, and...

Aha, this funny noise is NOT coming from my RF circuit, it's the common-mode noise coming from my USB port... 🤣

#electronics #hamradio #amateurradio

Even with a filter, the massive LO harmonics from the digital oscillator are still here... It seems the mixer is picking them up via capacitive coupling and radiation :blobcatsip: ... I should try adding a JFET buffer for better isolation and shield the LO completely...

#electronics #hamradio #amateurradio

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